TSTO (Two Stage To Orbit) is a candidate for advanced space transportation system, which is required to fly over a wide region from subsonic to hypersonic speed with an orbiter connected with a booster. The hypersonic flow field with aerodynamic interaction around a TSTO model, which consists of a delta wing as a booster and a hemisphere-cylinder as an orbiter, has been investigated. The temperature distribution is measured by the Temperature Sensitive Paint (TSP) method, and the heat flux with thermo-couples. As a result, the flow field has been significantly affected by the clearance between the two bodies. In the case of a small clearance, heat flux on the head of the hemisphere-cylinder becomes about 3.1 times as large as the stagnation heat flux for the hemisphere-cylinder alone. On the other hand, at a large clearance, heat flux on the delta wing becomes about 1.1 times as large as the stagnation heat flux. In addition, a new thermal protection system (TPS) to reduce the aerodynamic heating due to shock/shock interaction and shock/boundary-layer interaction is also investigated in this paper. A triangular prism installed on the delta wing can change the aerodynamic heating, depending on its location. It was found that a small device installed upstream is effective, where the heat flux has been reduced by about 48%.